Ambient Light Sources Research Articles

Transmission of Audio Signals by Infrared Light Carrier

A recently developed technique for the wireless transmission of audio signals makes use of the invisible modulated infrared radiation. Infrared emitting gallium-arsenide luminescence diodes are used as radiators of the modulated signal. As receiver, a photosensitive diode is used. Its plastic convex lens concentrates the incident infrared radiation on the rather small photosensitive diode surface. To eliminate the action of visible light, a so-called black filter — transparent only to infrared — is interposed. Amplitude modulation of the infrared emitter is possible, but cannot be used because other ambient light sources could create interference. To overcome this obstacle, frequency modulation of an amplitude-modulated standardized carrier frequency is used. The distribution of infrared radiators in a room is touched upon, and interference levels from ambient light sources are indicated. The components of a monophonic infrared audio transmission system are discussed.

Sinusoidal light stimulator using fluorescent tubes for the study of flicker perception

Fluorescent TL tubes were used in the construction of a sinusoidal light stimulator designed for the study of flicker perception. Amplitude response is linear and flat from d.c. to 90 Hz, without electro-optical feedback. A perfect temperature colour matching for the ambient and target light sources is easily obtained by using identical phosphors.